Heretofore an electrophotographic apparatus is known, in which a desired image is formed by forming an electrostatic latent image by means of an optical writing head using an LED, a liquid crystal shutter, EL, etc. on a photosensitive body and by developing this latent image and transferring it to a predetermined sheet.
In such a prior art electrophotographic apparatus there is disposed movably e.g. an endless photosensitive belt and in the neighborhood an on the outer side of this photosensitive belt there are disposed a charger, an LED head acting as the optical writing head and a developer. The electrostatic latent image is formed on the photosensitive belt by making the LED head emit light on the basis of a predetermined printing signal after having made the photosensitive belt writable by means of the charger. The desired image is formed on the sheet by attacking toner to this electrostatic latent image formed on the photosensitive belt by means of the developer to visualize it and by fixing the toner image thus obtained after having transferring it to the predetermined sheet.
Such an electrophotographic apparatus had a problem that, since the LED head is disposed on the outer periphery side of the photosensitive belt, in the case where scratches are produced on the surface of the photosensitive belt by a cleaner, etc., light coming from the LED head is diffused thereby and as the result the resolution of the latent image formed on the photosensitive belt is decreased.
For this reason there is known an electrophotographic apparatus, in which the LED head is disposed on the inner side of the photosensitive belt so that the latent image is formed by irradiating the inner side of the photosensitive belt with light. In such an electrophotographic apparatus, even in the case where scratches, etc. are produced on the surface of the photosensitive belt, the diffusion of the light is prevented and thus it is possible to form an image of high resolution.
However, in the prior art electrophotographic apparatuses described above, since the life of the photosensitive belt is relatively short with respect of the life of other members, it is necessary to exchange the photosensitive belt for every predetermined period. Therefore the photosensitive belt is constructed in the form of a cartridge so that the exchange operation for the photosensitive belt can be effected easily. However, since the LED head is disposed on the inner side of the photosensitive belt, it is necessary to dismount the LED head at the exchange of the photosensitive belt. Therefore not only the exchange operation for the photosensitive belt is extremely complicated, but also an operation for adjusting rigourously the position, where the LED head is mounted, is necessary for every exchange. In addition, it had a problem that it is feared to destroy the LED head at the mounting and dismounting thereof.